Conventional wafer containers, such as a Front Opening Unified Pod (FOUP) or a Standard Mechanical Interface (SMIF) pod, often contain shelves of fixed-pitch spacing to support the semiconductor wafers. FIG. 1 illustrates one embodiment of a conventional FOUP 10. The FOUP 10 includes a housing or shell 12 and a FOUP door 14 that mechanically couples with the FOUP shell 12. The housing 12, which includes a top 18, a back 20, a first side 22, a second side 24 and a bottom 26, defines an enclosure 28. The enclosure includes a support 30 located on the interior surface 32 of the first side 22 and the interior surface (not shown) of the second side 24. Each support 30 includes multiple shelves 16. Each slot between a pair of shelves 16 stores a single wafer. Each support 30 covers a portion of the wafer's peripheral edge while the wafer is seated in the FOUP 10. Access to the outside edge of the wafer is blocked by the shelf structure. Wafers are therefore typically handled by thin-bladed end effectors that must reach between adjacent wafers and subsequently either secure the wafer with a vacuum chuck or some type of edge support and/or gripping arrangement. These methods of securing the wafer often support the wafer by the wafer's back and front edges or elsewhere on the back edges.
This conventional wafer securing approach has been in widespread use in the semiconductor manufacturing industry for over twenty-five years. But this approach has a number of shortcomings that become more serious as the wafer size becomes larger. Also, increasing use is being made of thinned wafers, which are prone to significant bending deflections when supported by the edge.
Some of the deficiencies of conventional wafer support and carrier architectures include:
1) Wafer Mapping—Break-the-beam mapping has proven to be the most reliable method of determining a wafer's presence or absence and its vertical position within the container. However, break-the-beam mapping with the 300 mm FOUP architecture requires expensive and complex mechanisms to position sensing elements into the container.
2) End effector blade travel zone—To access a wafer, the end effector blade must first travel between adjacent wafers until it reaches a desired position, and at that position, lift the wafer from the support shelf. As wafer diameter increases, the mass of the wafer and the blade length required to support the wafer also increases. To maintain reasonable deflection characteristics of the end effector for larger diameter wafers, the end effector blade must be thicker. If the thickness of the end effector blade increases, the pitch between the wafers must also increase to allow the thicker end effector to pass between wafers without contacting the wafers. Either container size will have to increase or fewer wafers can be stored in conventional containers. Additionally, the extra travel length of the end effector is subject to wafer bow, distortion and warping, as well as the vibration characteristics of the end effector due to the rapid horizontal and vertical motions required for time efficient wafer handling. All of this must be accomplished without any accidental contact between a moving end effector and a wafer. Contact between the end effector and a wafer will likely to cause serious damage to sensitive circuits on the wafer as well as generating particle bursts that may contaminate all the other wafers in the container.
3) End effector travel path efficiency—A conventional end effector places a wafer in a container and then withdraws to enable vertical motion clearance for randomly accessing the next wafer, which is then withdrawn and taken to a process or metrology location. Thus, four horizontal moves are required for each wafer exchange at the container.
4) Process/Metrology chuck complexity—Typically, wafers are placed on flat chucks or platens for processing or measurement. In many applications, the wafer is secured to the chuck (and planarized) by applying vacuum. Use of conventional vacuum or edge grip end effectors necessitates large cutaway areas in the chuck to enable release of the wafer and withdrawal of the end effector blade.
5) Multiple wafer handling—It is very difficult in today's architecture to pick or place multiple wafers simultaneously or to enable individual selection of desired wafers in a mass transfer mode.
Thus, it would be advantageous to have an end effector with these features. The various embodiments of an end effector and a tine structure described herein provide such features.